Process for production of electrolytic manganese



Patented Aug. 3, l1948 nNlrsp l STATES PATENT OFFICE PROCESS FOR PRODUCTION-OF ELECTRO- LYTIC MANGANESE Dmitri Vedensky, Berkeley, Calif.

Application August 18, 1945, Serial No. 611,424

This invention relates to an improvement in an electrolytic process for the production of manganese and particularly to a process enabling `the anolyte to be re-used successfully.

A typical process for producing manganese electrolytically includes crushing and grinding of the ore, calcination followed by leaching with an eiiluent anolyte from the cells to which is usually added sulphuric acid and anhydrous ammonia. lThe slurry resulting from the leaching is thickened, the thickener overow being treated with a soluble sulphide to precipitate metals of the copper group which are removed.k The remaining solution is then treated with ferrous sulphate to remove arsenic, later being blown with air to remove iron. The remaining solution is then subject to electrolysis in a diaphragm cell, the diaphragm being provided by a suitable substance such as canvas. 'I'he solution fed to the cell for electrolysis contains manganese, ammonium sulphate, magnesium, calcium, sodium and potassium. An essential feature of the process is the necessity of maintaining a high concentration of .ammonium sulphate in the electrolyte. A concentration between 130- 140 grams of ammonium sulphate per liter may be considered as optimum. If the concen tration is permitted to drop below this value, electrolysis is seriously impaired' to a point where it stops altogether. Ii the concentration is raised, or if toomuch sodium or potassium is present, the current eiliciency is lowered undesirably. Electrolysis of this solutionresults in the manganese depositing on the cathode; sulphuric acid is generated in the anode cell compartment. The recovered anolyte contains, of course, unrecovered manganese as wellas a relatively large quantity of ammonium sulphate, sulphuric acid produced in the electrolysis t'o'- gether with the magnesium, calcium, sodium and potassium. It has been found that a continuous return of this anolyte resulted in the magnesium precipitating at various places in the process, usually as a complex salt plugging the diaphragm in the cell. Two methods arein use to prevent this condition. According to one method, the electrolyte is cascaded through a packed tower. A complex magnesium salt deposits on the packing, which is periodically removed and replaced. According to the other method, the anolyte is cooled to a temperature below any temperature occurring in the process so that the magnesium content is reduced to a point whereat, upon elevation of temperature of electrolyte, magnesium does not precipitate 5 Claims. (Cl. 2044-105)V i (see Patent 2,339,911). However,y cooling yol? anolyte also results in precipitation o f aconsid` erable portion of the ammonium sulphate present; in one operation, for each ton of magnesium recover, seven tons of ammonium sulphate were also removed as crystals. By this method, it is possible to reduce the magnesium content ofthe anolyte to about 6 grams per liter, butvery little crystallization of sodium and potassium salts occurs when these are present in the amount of less than 10 grams per liter of combined metals.

Experimenting with different oresI have observed that some of them contain appreciable amounts of sodium and potassium :compounds which are soluble in the electrolyte during leaching of manganese. Therefore, a plant treating such ores by thev electrolytic process must include some provisions for the removal of these salts as Well.

I have discovered several ways of meeting this condition. For example, sodium and potassium salts may be allowed to accumulate to the limit of their solubilities and removed from the electrolyte by cooling it by the same procedure as described above for magnesium.

Crystals formed by cooling will contain a com@ plex salt of the alkalis, manganese and ammonium y sulphate.

Another method includes bleeding off a portion of the anolyte, the amount of bleed-off depending upon the desired concentration of alkali metals in the electrolyte. Under certain conditions this method obviates the use of the cooling operation for the removal of magnesium. A

lThe use of either method, or of the combination of the two results in an appreciableloss of ammonium sulphate from the circuit.

I have found that the anolyte bled off can be treated to recover the ammonia present so that the value of this, otherwise lost when the cooling operation is practiced, is recovered in a usable form. I have discovered that if t0 the spent bled off anolyte is'added lime or other suitable material andthe resulting mixture heated and' agitated, the ammonium sulphate is decomposed and NH3 is evolved oil" as a gas. This is passed through a packed tower through which anolyte, preferably acidilied with additional sulphuric acid, is circulated, the refreshed anolyte then bee ing returned to storage for subsequent re-use. In caseit is desired to utilize the cooling operation as well, some or all of the dry crystals re' covered from this can be added to the agitator and the valuable ammonia contentv presentin these recovered instead of being wasted as hereconditioned for use and the concentration of such i impurities as magnesium, sodium and potassium, otherwise adversely aifecting the operation, kept below the maximum permissible concentration.

The invention will become further apparent upon consideration of the attached drawing and 36 to anolyte storage tank 9, a portion of the anolyte being bled oif through line 3'I to the agitator I2 Where it is treated with lime and steam to provide effluent ammonia gas. If desired, a portion of the crystals produced can also be added to the agitator as is indicated by line 38 to evolve and recover the ammonia present.

In case the removal of alkalis and magnesium is accomplished entirely by cooling and no bleedoff is practiced, the separated crystals are dissolved in an agitator and similarly treated for evolution and recovery of ammonia. This is the following description of a specific operation conducted in accordance with the present invention. In the drawing accompanying and forming a part hereof, Figures 1, 2 and 3 are ow sheets and diagrams illustrating how the anolyte can be processed according to this invention. A's` appears in Figure i in the drawing, anolyte from electrolytic cell 6 is taken oir through line 'I to anolyte storage tank 9. A portion of the anolyte is bled olf through line I I into an agitator I2, calcium oxidebeing added at I3. Steam is supplied 'by line I4 to the agitator to heat the slurry until ammonia gas results from the decomposition of the ammonium sulphate. The ammonia gas is taken 01T through line I6 and is passed through a packed tower II through which anolyteis circulated from tank 9 through line I 8, the material remaining in the agitator being discarded or otherwise utilized. Sulphuric acid is added through line I8 and the refreshed anolyte is returned through line 2l to the tank 9. The reactions involved are as follows:

These show the quantities` required. The decomposition to NH3 is usually about 97% when the slurry is heated tol about 200 F.

4In one specic operation conducted in accordance with this invention it was found that 11.6% of anolyte circulating in line 'I had to be bled off to maintain combined sodium and potassium concentration at 1-0 gra-ms per liter.

The anolyte bled oir contained 15 grams of manganese, 135. grams of ammonium sulphate and 40. grams of sulphuric acid per liter.

To anolyte bled off through line Il. to agitator IZ, calcium. oxide. was added in the amount of The mixture was heated in 80.1 grams per liter. the agitator for one hour to temperatures. ranging 190 C.-f200 C. Liberated ammonia was absorbed in spent anolyte. It was found that 97% of the ammonia fed to the agitator was liberated as gas and was absorbed in the spent anolyte.

In case the magnesium content of the ore is suciently high or if, for some other reason, removal of the magnesium is desirable as a separate operation, 'the spent anolyte is passed from line I directly into mixing tank 8, as in Figure 2, to which additional ammonium sulphate is usuallyl added. The resulting solution is then passed tothe magnesium removal tank wherein` the temperature is lowered by circulation of a suitable refrigerating medium such as cold water and the magnesium crystallized as a, complex salt. The resulting crystal slurry is then passed through line. 33 into a centrifuge 34. The separated anolyte is removed fromA the centrifuge through 1in-e shown in Figure 3 vwherein the crystal mixture "is passed`r` fromline 31 to a dissolving tank 4I wherein the crystal mixture is dissolved in water and thensent on to agitator I2 for treatment with lime and heat.

' i In place of calcium oxide one can use the oxides ci other materials such as magnesium or manganese, or caustic material such as NaOH and KOH. Any oxide or hydroxide can be utilized which results in formation of the corresponding sulphate and ammonium hydroxide, the latter being decomposed on heating. i

The liberated ammonia gas does not necessarily have to be absorbed in acid although this appears to be the simplest method. The ammonia gas can be returned to the process at some other point, for instance to the leaching agitators for the final adjustment of the pH of leach liquor, or it may be compressed and stored as liquid ammonia and subsequently used wherever desired.

Iclaim:

l. In a process for recovering manganese electrolytically from a solution containing manganese sulphate, the steps comprising bleeding off a. portion of a stream of a manganese lean anolyte containing ammonium sulphate, manganese sulphate, sodium sulphate` potassium sulphate and magnesium sulphate, adding a material selected from the group consisting of a metallic oxide and a metallic hydroxide to the bleed- 01T' stream to convert the ammonium sulphate therein to ammonium rhydroxide and' the corresponding metallic sulphate, heating the ammonium hydroxide toevolve gaseous ammonia and toleave behind as a residue the other constituents of the bleed-01T stream and said metallic sulphate, adding sulphuric acid to at least a portion of the anolyte stream, and absorbing the evolved ammonia gas in the sulphuric acid containing anolyte stream to re-form ammonium sulphate therein.

2. In a process for recovering manganese electrolytically from a solution containing ammonium sulphate and manganese sulphate, the steps comprising cooling a stream of manganese lean anolyte containing ammonium sulphate, manganese sulphate, sodium sulphate, potassium sulphate and magnesium sulphate to precipitate a crystal mixture including magnesium and ammonium sulphate, separating the remaining anolyte stream from the so formed crystal mixture, evolving ammonia from the separated crystal mixture, adding sulphuric acid to a portion of the anolyte stream., and absorbing the evolved am monia in said portion of the anolyte stream.

3. In a process for recovering manganese electrolytically from a solution containing ammonium sulphate and manganese sulphate, the steps comprising cooling a stream of manganese lean anolyte containing ammonium sulphate, manganese sulphate, sodium sulphate, potassium sulphate and magnesium sulphate to` precipitate a crystal mixture including magnesium and ammonium sulphate, separating the anolyte stream from the crystal mixture, adding Water and a material selected from the group consisting of a metallic oxide and a metallic hydroxide to the separated crystal mixture to form ammonium hydroxide therein, heating the so formed mixture to decompose the ammonium hydroxide and evolve gaseous ammonia therefrom, adding sulphuric acid to a portion of the anolyte stream and absorbing the evolved ammonia in said portion of the anolyte stream.

4. In a process for recovering manganese electrolytically from a solution containing ammonium sulphate and manganese sulphate the steps comprising cooling a stream of manganese lean anolyte containing ammonium sulphate, manganese sulphate, sodium sulphate, potassium sulphate and magnesium sulphate to precipitatea crystal mixture including magnesium and ammonium sulphate, separating the anolyte stream from the crystal mixture, bleeding off a portion of the separated anolyte stream, mixing the bleed-off portion with the separated crystal mixture, evolving ammonia from the so formed mixture of bleed-oir and crystals, adding sulphuric acid to the remaining separated anolyte stream, and absorbing the evolved ammonia in the sulphuric acid containing separated anolyte stream to restore the ammonium sulphate content thereof.

5. In a process for recovering manganese electrolytically from a solution containing ammonium sulphate, manganese sulphate, sodium sulphate, potassium sulphate and magnesium sulphate, the steps comprising cooling a stream of manganese lean anolyte containing ammonium sulphate, manganese sulphate, sodium sulphate,

potassium sulphate and magnesium sulphate, to 5 precipitate a crystal mixture including magnesium sulphate, sodium sulphate, potassium sulphate and ammonium sulphate, separating the anolyte stream from the crystal mixture, bleeding off a portion of the separated anolyte stream, mixing the bleed-01T with separated crystal mixture, adding water and a material selected from the group consisting of a metallic oxide and a metallic hydroxide to the so formed mixture of bleed-ofi` and crystals, adding sulphuric acid to the separated anolyte stream, heating the so formed mixture to decompose the ammonium hydroxide therein and evolve gaseous ammonia therefrom, and absorbing the evolved ammonia in the sulphuric acid containingseparated anolyte stream to restore the ammonium sulphate content thereof.

DMITRI VEDENSKY.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS 

